CFD modeling of fish exclusion screens (#24)

Fish screens or exclusions are a common design option to prevent the movement of aquatic organisms into hydroelectric, irrigation or other types of water withdrawal structures. To ensure proper functioning of the exclusion screens, state and federal agencies have regulatory requirements for the hydraulic conditions near the screen. These include limitations on the allowable velocity components normal (approach velocity) and tangential (sweeping velocities) to the screen. Approach velocities must be limited to prevent the impingement of fish on the screens, while minimum sweeping velocities are required to prevent debris build up. Additional design targets include ensuring uniformity of flow over the surface of each screen.

In the current practice, physical laboratory tests are often required in the design stage to ensure that the exclusion screens meet regulatory requirements for target species. However, the progress made with commercially available Computational Fluid Dynamics (CFD) tools, in conjunction with improvements with available computational hardware, allow us now to envisage using such numerical modeling solutions for detailed studies of fish screen hydraulics.

In this study we evaluate using a CFD model as a design tool for fish exclusion screens. Drawing on measured data from fish screens tested at the United States Bureau of Reclamation (USBR) hydraulics laboratory, we validate the results of a numerical model with measured USBR data, and evaluate the range of model setup options using both porous objects and porous baffles to represent the screens. We evaluate numerical options and discuss how these can be defined to maximize the accuracy and efficiency of the simulation.